Measurement of Si self-diffusion coefficients of wadsleyite as a function of water content
Final Report Abstract
In this project, we synthesized large single crystals of wadsleyite, and measured their Si and O selfdiffusion coefficients. The new insights through this experiment are as follows. (1) The activation energy of Si diffusion in wadsleyite with a couple of thousands ppm water is just half of that with several tens ppm water. (2) The water-content dependence of the Si self-diffusion coefficient has large anisotropy. (3) The water-content dependence of Si self-diffusion coefficient is quite large. Even in the direction in which the water-content dependence of Si self-diffusion coefficient is the smallest, it is twice larger than that of forsterite. (4) Dehydrated crystals exhibited much larger Si self-diffusion coefficients than undehydrated crystals. (5) In contrast to Si, the O self-diffusion coefficient has no water-content dependence in the a- and b-directions. (6) The Si self-diffusion coefficients are larger than the O selfdiffusion coefficients at water contents higher than 1000 ppm. In this case, the O diffusion rather than the Si diffusion could be a rate limiting process in rheology.
